Scientists have found clues to why people develop high cholesterol levels - an important cause of heart disease.

Researchers in the United States have identified a protein which they say plays a key role in determining whether or not fatty substances and cholesterol build up inside the arteries.

Tests on mice have shown that these substances are more likely to build up when this protein is switched off.

Their discovery could help in the development of new drugs to fight cholesterol and heart disease.

Key protein

Dr Joachim Herz and colleagues at the University of Texas Southwestern Medical Center in Dallas looked at a protein called
low-density lipoprotein receptor-related protein (LRP1). It plays an important role in the development and growth of blood vessels.

The researchers switched off this protein in mice. They found that this led to an increase in the cells needed to create blood vessels.

However, it also meant that the wall inside the vessels were more susceptible to the build-up of cholesterol.

In humans, an increase in cholesterol and fatty substances inside blood vessels can lead to blockages. This, in turn, can trigger a heart attack or a stroke.

According to the researchers, the LRP1 protein is unlikely to ever be switched off in humans.

However, the tests on mice suggest that even small changes could trigger higher cholesterol levels.

The researchers also discovered that a drug used to treat leukaemia can reduce the build-up of cholesterol and fatty substances or atherosclerosis inside the arteries.

Gleevec is used to treat patients with chronic myeloid leukaemia. It works by stopping cancer cells from dividing and growing.

The researchers found that it can also prevent problems in vessels which can contribute to the build-up of cholesterol in mice.

"We effectively found that Gleevec could reduce atherosclerosis in our mouse models by 50%," said Professor Herz.

While the drug is too powerful to be given to people with high cholesterol, it could provide scientists with clues to fighting heart disease.